This invention relates to automated processing workstations and, more particularly, to methods and apparatus for fluid level detection. The invention has application, for example, in the automated testing, synthesis and processing of biological samples, chemical compounds, and the like.
Historically, nearly all biological and chemical laboratory work was performed manually by scientists and/or laboratory technicians. Recently, however, several factors have made it impractical, if not impossible, to continue to perform the bulk of such work manually. These factors include the tremendous growth of biotechnology and the pharmaceutical industry, and the corresponding demands for increased laboratory throughput and accuracy.
Fortunately, the robotics industry has developed automated equipment and workstations that can be entrusted to handle many laboratory functions. Despite the advantages of such equipment, some functions remain unduly expensive.
One example is pipetting and, in particular, immersing a pipette tip in a fluid. Although this is a routine task when performed manually, it can tax automated processing equipment. In particular, when an individual pipettes a fluid, he or she must ascertain its level in a container in order to ensure that a pipette tip is placed far enough into the container to reach the fluid, yet not too far so as to risk tip and/or container breakage.
Automated pipetting equipment currently available for sensing fluid level is expensive. One system requires pipettes that are equipped with carbon tips. By measuring changes in capacitance, the system can sense fluid at or near the tip. Unfortunately, the carbon tips can be up to 10 times as expensive as conventional plastic tips. Given the frequency with which tips need to be replaced, the increase in tip cost can be unacceptable.
An object of the present invention, accordingly, is to provide improved methods and apparatus for automated processing workstations.
A more particular object of the present invention is to provide an automated workstation capable of continuous, high throughput and high accuracy processing of biological, chemical and other specimens and compounds.
Another object of the present invention is to provide a fluid level sensing system that may be easily implemented or retrofitted into existing automated processing workstations with minimal associated costs. A further object of the present invention is to provide a fluid level sensing system that is compatible with future automated processing workstations.
Yet another object of the present invention is to provide a fluid level sensing system that provides for large-scale pipetting procedures while maintaining acceptable levels of accuracy and safety.
Still another object of the present invention is to provide a fluid level sensing system for use in conjunction with automated pipetting procedures that minimize the risk of damage to equipment and specimens.
Still yet another object of the present invention is to provide a fluid level sensing system that facilitates immersion of pipette tips (or portions of other processing apparatus) in a fluid, yet, prevents risk of breakage of the tips or the containers in which the fluid is disposed.
The foregoing objects are among those attained by the present invention, which provides a fluid level detection system, e.g., for use in the processing of biological and chemical samples. While the invention is primarily shown and described as pertaining to automated processing procedures such as pipetting, it is applicable to any procedure in which sensing the level of a fluid is desired.
The fluid level detection system of the present invention includes an illumination source and a photodetector, which are aimed toward the liquid and generally angled toward one another. The illumination source produces a beam, which the photodetector is adapted to sense as it reflects from the surface of a fluid. The photodetector output varies in accord with the amount of reflected radiation that impinges on it. That output, in turn, varies as the photodetector (and illumination source) gets closer to the surface of the liquid, increasing then decreasing as the reflected beam moves from overshooting the undershooting the photodetector.
In an exemplary aspect of the present invention, the illumination source and the photodetector are coupled to a pipette tip or other such element. As the tip moves towards the fluid, the photodetector output increases, peaks and decreases to define a pulse-shaped output curve.
The illumination source and the photodetector can be aimed at a point located a predetermined distance, for example, a few millimeters, in front of the tip of the element. This results in the output curve peaking prior to the tip contacting the surface of the fluid. By observing when that peak occurs (and, more generally, by observing the curve itself), the distance between the element tip and the fluid can be readily ascertained.
Further aspects of the invention provide methods of liquid level sensing corresponding to the operations as described above.